NEW DELHI: Pakistan is focusing on building low-yield, tactical nuclear weapons which it can use in case of skirmishes at the border with India. After disclosures that Pakistan is building its fourth reactor at the Khushab military facility, fresh estimates made by security and intelligence officials here suggest that Pakistan now has the capability to add 8-10 such weapons in its kitty every year.

The figure is likely to go up considerably once the new reactor becomes operational in less than two years. Latest satellite images revealed recently that Pakistan has expedited work on the fourth reactor, a plutonium producing facility.

The news is a surprise, if not shock, to the government here. Its belief, based on assessment by top scientists, was that Pakistan was unlikely to undertake this sort of expansion as it did not have enough uranium.

Pakistan is internationally acknowledged to have a nuclear arsenal of 100 weapons but the recent focus on low-yield, also known as tactical, weapons has become a source of worry for India.

Former chief of joint intelligence committee S D Pradhan, who has closely followed Pakistan's nuclear-weapon program, says Pakistan's desire for such weapons is one of the main reasons for the acceleration of its nuclear program.

"They are following the Chinese model of having low-yield nuclear weapons. Pakistan believes these weapons will provide it a flexible response in case of an escalation with India and allow it to dominate," says Pradhan.

Officials and experts believe Pakistan will use it only in the case of any incursion made by Indian forces into Pakistani territory or what is known as India's cold start doctrine. In the event of another Mumbai-like terrorist attack, there is going to be real pressure on India to mount such an incursion and strike some of the terror camps.

Indian officials said the manner in which Pakistan has carried out work on the fourth reactor, of which there was no trace as late as 2009, suggest a constant supply or uranium and that this could only have been made possible by China. "The cost involved is too high and then, of course, the amount of uranium required. It's too much for Pakistan to achieve without support from China," said a senior government official.